In GB Patent No. 558115 there is proposed an opposed-piston internal combustion engine in which two pistons are moveably fitted in a cylinder so as to oppose one another, and two crankshafts are connected to the pistons via connecting rods.
As shown in FIG. 12 hereof, the two crankshafts 201, 202 are disposed in parallel in a crankcase 200. The cylinder 203 is provided to the crankcase 200 so as to be disposed between the crankshafts 201, 202, so that the cylinder axis is perpendicular to the crankshafts 201, 202. Pistons 204, 206 are moveably inserted into the cylinder 203 from openings on either end thereof. A yoke 207 is integrally formed with an end part of the piston 204. The yoke 207 is connected to the two crankshafts 201, 202 via connecting rods 208, 208. A yoke 211 is integrally formed with the end part of the piston 206. The yoke 211 is connected to the two crankshafts 201, 202 via connecting rods 212, 212. The spaces between the cylinder 203 and the pistons 204, 206 are sealed using a plurality of piston rings 214 attached on the pistons 204, 206. A combustion chamber 216 is formed between the two pistons 204, 206.
Since the piston rings 214 are attached on the pistons 204, 206, ring flutter occurs at high engine speeds from the piston rings 214 that vibrate within the ring grooves of the reciprocating pistons 204, 206. As a result of the ring flutter, during the power stroke, combustion gas in the combustion chamber 216 passes between the cylinder 203 and the pistons 204, 206; i.e., between the cylinder 203 and the piston rings 214. The gas is blown into the crankcase 200, and the amount of blow-by gas increases.
When the pistons 204, 206 move in a reciprocating manner, the volume of the crankcase 200 varies, and the pressure inside the crankcase 200 fluctuates. Therefore, when ring flutter occurs, oil mist inside the crankcase 200 passes between the cylinder 203 and the pistons 204, 206, i.e., between the piston rings 214 and the cylinder 203 during the intake stroke, and readily penetrates into the combustion chamber 216.
A demand has accordingly arisen for an internal combustion engine in which it is possible to prevent the incidence of ring flutter, and oil mist penetrating into the combustion chamber.